A variety of electroplating baths have been disclosed for the electrodeposition of bright tin upon metallic substrates. These baths have been substantially acidic and have been utilized in many industrial applications. Typical of such disclosed baths include those described in U.S. Pat. Nos. 3,361,652; 3,471,379 and 3,875,029.
Many of these aforementioned baths contain as surface active agents imidazoline derivatives, which tend to provide instability to the bath. Furthermore, the baths aforementioned typically contain a single carbonyl compound as a brightener. While these baths have proven generally satisfactory, and have been widely utilized in a commercial setting, they are usually deficient in one or more desirable operating characteristics, and the deposits produced thereby frequently fail to provide a balance of characteristics such as smoothness, brightness, adherence, solderability and stability to resist aging. Furthermore, these baths typically do not exhibit the aforementioned characteristics over the entire operable range of current densities and do not avoid step plating and shadowing when holes and deep recessed areas are present in the metallic work piece utilized in the bath.
Therefore, while various of the baths described in the literature are operable with varying degrees of effectiveness, there has remained a need to provide a bath capable of producing smooth adherent deposits exhibiting spectral brightness over a wide current density range and wherein the components of the bath provide substantial stability thereto.
It has now been determined that by utilizing a specifically defined combination of organic brighteners, an acid tin or tin-cadmium alloy electroplating bath is provided which is substantially stable and is capable of producing bright, smooth, fine-grained deposits over a wide cathode current density range upon continued electrolysis. Furthermore, superior bright throwing power in recessed areas of the cathode is exhibited. Since the bath is free of ammonium ion and cyanide/or chelating compounds, simplification of waste treatment procedures necessary for removal of the metals from the bath is exhibited.